One of the ways that seven-card stud is different from hold'em is your ability to read hands.
In hold'em, hand reading relies on considering your opponent's betting, his image and the board. There is no need to remember folded cards, nor to consider them when reading your opponent. Similarly, there is no need to consider the individual exposed cards of your opponent, as you share the same board.
That's not the case in seven-card stud. The extra layers of information contained in the folded cards and in your opponent's individual (and developing) board make hand reading much more complicated in stud than in hold'em.